The invention generally relates to the field of imaging colorimeter applications, for example in the display manufacturing industry.
Imaging colorimetry-based testing systems have demonstrated to be successful in improving quality and reducing production costs for all types of flat panel displays, like LCD displays and LED display screens. Testing applications span the color matrix displays of smartphones, tablets, laptops, monitors, TVs etc.
Key components of known display testing environments are so-called imaging colorimeters, which provide accurate measurement of display visual performance that matches human perception of brightness, color, and spatial relationships. High-performance imaging colorimeters can accurately measure the color, the luminance (brightness) of individual pixels in a display as well as overall display uniformity.
In a typical manufacturing process, display visual performance is tested by automated inspection systems employing such imaging colorimeters. This has several advantages. A quantitative assessment of display defects is feasible, an increased testing speed can be achieved, and, most importantly, a simultaneous assessment of full display quality, i.e. uniformity and color accuracy is possible.
Generally, spectral photometers (also referred to as spectrophotometers) and photoelectric colorimeters are used for the measurement of chromaticity and luminance. Photoelectric colorimeters have optical filters approximating the tristimulus values, and measure the chromaticity and luminance by detecting the intensity of the light passing through these optical filters. A spectral photometer measures chromaticity and luminance by separating the light from the sample into wavelength components using, for example, a prism or a diffraction grating or a spectral filter and detecting the intensity of each primary wavelength element. As a result, a spectral photometer is capable of accurately measuring absolute chromaticity and luminance. However, the construction necessary for performing spectral separation is complex, which makes the equipment large in size as well as expensive.
An imaging colorimeter system is for example known from U.S. Pat. No. 5,432,609. In the known system, an optical filter means, which allows only certain wavelengths to pass through, is located in front of a first light receiving means which receives the light from multiple points on a sample to be tested. In this way, the chromaticity and luminance at the multiple points on the sample is measured with spatial resolution by a simple method using the same principle as that employed by a photoelectric colorimeter. Moreover, a spectral separating means which separates light into primary wavelengths is located in front of a second light receiving means which receives the light from one prescribed point among the above multiple points, i.e. without spatial resolution. Hence, the chromaticity and luminance at the above one prescribed point among the multiple points is accurately measured by a spectrophotometer-type instrument. The measurements for the multiple points on the sample, which are output from the photoelectric colorimeter-type first light receiving means, are corrected based on the accurate measurement output from the spectral photometer-type second light receiving means.